Find the following properties of the data in the (built-in) dataframe sleep:

• The classes of the different variables. Store this result in a vector called classes.
• The 5, 25, 50, 75 and 95 percentile for all numeric variables. Store this result in a matrix called percentiles.
• The number of unique values for the factor variables. Store this result in a vector called uniques.
• The mean value of the numeric column extra for every combination of possible levels of the factors group and ID. Store this result(s) in a matrix called means.